Opus audio format is not natively supported by iOS. Fixing documentation.

@llfbandit According to Apple Developer docs, opus codec is supported on iOS 11+ using kAudioFormatOpus for AVFormatIDKey.
https://developer.apple.com/documentation/coreaudiotypes/kaudioformatopus

record_darwin specifies this here:

Opus is available for decoding only.

Opus is available for decoding only.

@llfbandit I edited this file:

I added the line: AudioEncoder.opus.rawValue

I then tried recording using AudioEncoder.opus on iOS, and the recording was successful. Reading the first bytes of the output file I can see that it was recorded in a CAFF container, which is what is expected for iOS.

So I believe iOS does support opus as an encoder (and the documentation of the package was correct in saying SDK 11+), but the record_darwin package left out the opus format in the isEncoderSupported function.

Can you send me a simple audio file with this setup?
If I remember well, the underlying encoder was not opus. Maybe I'm wrong?

I used the following config:

RecordConfig(
  encoder: AudioEncoder.opus,
  sampleRate: 16000,
  bitRate: 8000,
  numChannels: 1,
)

After recording an audio file, I analyzed it with ffprobe:

Input #0, caf, from '1.caf':
  Duration: 00:00:08.66, start: 0.000000, bitrate: 37 kb/s
  Stream #0:0: Audio: opus (opus / 0x7375706F), 48000 Hz, mono, fltp

For some reason the bitrate and sample rate are not correct, but it is working in opus format.

Ok, that's good news!
I'm not very surprised if iOS does not support those values.

The only caveat here (before testing & re-introducing this encoding) is CAF. This container is only supported by Apple products/platforms.

Yes, ideally there would be a solution to convert to OGG container, but I can figure something out for that.

Another funny thing, Safari only supports opus in CAF container and not OGG.
Welcome to my world :)